Proline occupies a special role among those amino acids incorporated into peptides and proteins by the normal ribosomal pathways as it is the only residue which leads to an N-alkyl amide bond. In peptide natural products which often have special biosynthetic pathways, or unusual post-translational modifications, N-methyl amino acids are common and may play a special role because of their conformational properties including their proclivity for cis-trans isomerism of the amide bond. Marshall et al. proposed the 1,5-disubstituted tetrazole ring system, Y[CN4], as an alternative way of mimicking the cis-conformation of a peptide bond. This paper demonstrates conversion of dipeptides to analogs containing the 1,5-tetrazole ring replacing the amide bond.